Method of forming tapered threads



Jan. 17, 1928. 1,656,594

- J. D. MERRIFIELD METHOD OF FORMING TAPERED THREADS Filed Feb. 1 1925 14 won bdr- Patented Jan. 17, 1928.

UNITED STATES esasei .PATENT OFFICE.

JOHN MERRIFIELD, or ERIE, PENNSYLVANIA, ASSIGNOR r0 REED ANUFACTUR- ING GOMPANY, OFERlZE, PENNSYLVAN IA, A CORPORATION OF PENNSYLVANIA.

METHOD OF FORMING TAPERED 'rHREAfis;

Application filed February the thread and ma ing a very much more desirable chip. In cutting such a thread it is necessary to have the finished thread largely under, or along the tool cutting the thread and inasmuch as the cutting is done entirely on one of the slopes, preferably the rear slope of the thread as itisfcut, it

isnecessary to vary the lead of the toolcutting the thread so as to compensate for the shift in the trough of the thread formed with each succeedingcut, in other words, the lead should increase at least equal to the thickness of the out. In carryingout my method also I prefer to cut the initial threads with one wall at a slightly different angle than the other walls in order that the thread may be more readily started so that with this method it is feasible to start the die, or cutting tool, without the use of the ordinarylead screw; I y I In the accompanying drawings I have exemplified my invention as being applied to the cuttingof an external thread but it will be understood that I do not wish to be so limited. The die by which the method may be practiced is illustrated in the accompanying drawings as follows Fig. 1 shows a side elevation of a chaser starting on a cut on the pipe.

Figlfl a similar view with the chaser progressed slightly farther.

Fig. 8a similar view with the out of the thread completed.

Fig. 4 a diagrammatical view showing the relation of teeth of the cutting chaser and the threads cut.

Fig. 5 an enlarged view showing the succeeding cuts made as they are made.

Fig. 6 an elevation of a die in which the chasers may be mounted. 1 marks the chaser, 2 the body of the die, and 3 a bar, or pipe out. The chasers of the die havethe finishing teeth 4 with the crests 4 and troughs 4", the starting teeth 5 with the crests 5 and the troughs 5", and the line entering teeth. 6 having the crests 6 19, 1923. Serial No. 619,880.

lines (6 indicate the relation of the crests of the teeth with the troughs of the teeth bein cut, lines 6 each extended from the tootfi of the finished cut to the tooth forming the cut, a line o0 arallel to the axis and radially positioned tooth of smallest diameter of the chasend points of intersection between the lines a and 0 and e pomts'of intersection between the lines I) and 0. iThe distance between the polnts e and d is slightly less than the distance between the crests 4e. This variation indicates the difference between" the lead of the teeth of the die and the spiral of the thread cut, the distance between the points e indicating the pitch of the thread of the tool and the distance between the points d m tlicating the pitch of the thread as actually cu The pipe ordinarilyas cut oif has a burr 11 and the entering teeth 6 are particularly deslgned to engage and pass this obstruction. The starting teeth form a small spiral groove 12 in the bar, leaving a fiat crest 13. TlllS is the reverse of the ordinary manner of cutting threads with dies in that ordinarily the entering or starting teeth out a flat trough and leave hair-like threads on the bar. Thedifliculty with this method is that these threads have not sufiicient subcien't. metal to prevent strippingand it is consequently possible to start the die without the ordinary leadscrew.

l[he threads cut on the pipe have the ores along the crest of the- 1 1,.tr0ughs 15, the forward slope 16 and rearward slopev 17. It will be noted that as the 'threadsand the initial work are die progresses the cut is taken. from the front slope of the thread entirely but a with each passage of .the die until the slopes meet in a point at the final crests these started the crests 14 are flat and as the" threads with the flat crest are thefinal threads and as. noted correspond with the trough of the die. The spiral of these finished threads,- however, are not the same as the spiral of the die, the spiral die varying from the spiral of the finished thread in accordance with the thicknessof the shaving removed where it on the front slope. As

and troughsfi As shown in Fig, a dash preferred and shown the lead of the die. in liq as much greater as the finished thread as the thickness of the shaving.

The successive cuts are shown in Fig. 5, the entering teeth making a cut of material indicated at 18, the starting teeth making cuts indicated at 19 and the teeth 4 a series of ribbon-like cuts as indicated at 20,

It will be observed that the peaks of the teeth in the die correspond with the troughs of the finished thread and inasmuch as the cutting is done entirely along the front slope of the thread the lead of the teeth in the cutter is as much greater than the lead of the threads being cut as the thickness of the out in one rotation so that the troughs of the thread out are properly spaced under the die. Thus the variation in pitch which the cutting from one slope alone would bring about is rectified so that the troughs of all the finished threads are properly s aced from the deepest cut to the most sliallow cut. I prefer to make the entering threads finer but of the same lead as the other threads. Ordinarily there are two threads in the same space as occupied by one thread of the ordinary cutting thread and I prefer to make the starting threads with -the cutting face inclined to the finished thread so that it will more readil wedge on to the pipe and thus facilitate t e starting of the die on the pipe. This is done while still maintaining the troughs be tween the threads in proper relation.

What I claim as new is 1. The method of forming tapered threads which consists in cutting a spiral groove by cuts simultaneously made at a plurality of points at intervals about the axis and of a lead difi'erin from the finished thread and cutting one s ope of the groove to finish the thl read.

2. The method of forming tapered threads which consists in cutting a spiral groove by cuts simultaneously made at a plurality of points at intervals about the axis and of a lead differing from the finished thread and cutting one slope of the groove to finish the thread and rectifying the pitch with the Cut;

3.' The method of forming external tapered threads which consists in cutting a spiral groove by cuts simultaneously made at a plurality of points at intervals about the axis'and of alead differing from the finished thread and cuttingone slope of the groove to finish the thread. y I 4. The method of forming external ta pered threads which consists in cutting a spiral groove by cuts simultaneously made at a plurality of points at intervals about the axis and of a lead differing from the finished thread and cutting one slope of the groove to finish the thread and rectifying the pitch with the cut.

5. The method of forming tapered threads which consists in making a plurality of cuts in tapered relation from one slope of the thread and completing the threads simultaneously and rectifying the pitch of the finished thread by varying the spiral of the cut.

6. The method of forming external tapered threads which consists in making a plurality of cuts in tapered relation from one slope of the thread and completing the threads simultaneously and rectifying the pitch of the finished thread by varying the spiral of the cut.

a 7. The method of cutting tapered threads which consists in making a plurality of cuts at intervals about the axis and along the axis upon one slope of the threads and c0mpleting the threads simultaneously and rectifying the pitch of the finished thread by varying the spiral of the cut.

8. The method of forming tapered threads which consists in cutting a spiral groove of a lead differing from the finished thread, cutting one slope of the groove to finish the thread and completing the threads simultaneously, the starting out on the slope being at an inclination differing fromt e succeeding cuts.

9. The method of forming tapered threads which consists in cutting a spiral groove of a lead differing. from the finished thread, cutting one slope of the groove to finish the thread and completing the threads simultaneously, the starting out on the slo e being at an inclination less abrupt than t e succeeding cuts;

10. The method of forming external tapered threads which consist in cutting a 11. The method of Iorming external tapered thread'swhich consists in cutting a spiral groove of a lead differing from the finished thread, cutting one slope of the groove to finish the thread and completing the threads simultaneously, the starting cut on the slope being at an inclination less abrupt than the succeeding cuts.

In testlmony whereof I have hereunto set my hand. i

. v JOHN D. MERRIFIELD.

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